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NEET PHYSICSWAVE OPTICSMedium

Question

A uniform rope of length LL and mass m1m_1 hangs vertically from a rigid support. A block of mass m2m_2 is attached to the free end of the rope. A transverse pulse of wavelength λ1\lambda_1 is produced at the lower end of the rope. The wavelength of the pulse when it reaches the top of the rope is λ2\lambda_2. The ratio λ2λ1\frac{\lambda_2}{\lambda_1} is:

A

m1+m2m1\sqrt{\frac{m_1+m_2}{m_1}}

B

m2m1\sqrt{\frac{m_2}{m_1}}

C

m1+m2m2\sqrt{\frac{m_1+m_2}{m_2}}

D

m1m2\sqrt{\frac{m_1}{m_2}}

Step-by-Step Solution

  1. Wave Speed on a String: The speed vv of a transverse wave on a string under tension TT is given by v=Tμv = \sqrt{\frac{T}{\mu}}, where μ\mu is the linear mass density of the string .
  2. Relationship between Wavelength and Tension: Since the frequency ff of the wave remains constant as it propagates, the wavelength λ\lambda is directly proportional to the wave speed vv (because v=fλv = f\lambda). Thus, λT\lambda \propto \sqrt{T}.
  3. Tension at the Bottom (T1T_1): At the lower end of the rope, the tension is entirely due to the weight of the attached block of mass m2m_2. Therefore, T1=m2gT_1 = m_2g.
  4. Tension at the Top (T2T_2): At the upper end (at the rigid support), the tension must support the weight of both the rope and the attached block. Therefore, T2=(m1+m2)gT_2 = (m_1 + m_2)g.
  5. Calculate the Ratio: Using the proportionality λT\lambda \propto \sqrt{T}, the ratio of the wavelengths is: λ2λ1=T2T1=(m1+m2)gm2g=m1+m2m2\frac{\lambda_2}{\lambda_1} = \sqrt{\frac{T_2}{T_1}} = \sqrt{\frac{(m_1 + m_2)g}{m_2g}} = \sqrt{\frac{m_1 + m_2}{m_2}}

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from WAVE OPTICS. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSWAVE OPTICSuniformlengthverticallysupportattached

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